Differential diagnosis of mesenchymal neoplasms of the digestive tract by cell block and immunohistochemistry.

Objectives: To evaluate the diagnostic yield of the cell block (CB) technique with immunohistochemistry in patients with mesenchymal neoplasms of the gastrointestinal tract collected by endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA).

Methods: Tissue samples from consecutive patients with subepithelial lesions collected by EUS-FNA, without analysis by on-site cytopathology, were evaluated by the same pathologist only using CBs in AAF fixative. Sections were stained with haematoxylin-eosin and underwent complementary immunohistochemical staining for SMA, CD117, DOG-1 and S100 in the presence of mesenchymal neoplasms. Specimens were defined as diagnostic when sufficient tissue was present for histopathological evaluation and immunohistochemistry analysis. If they were insufficient for complete evaluation, the specimens were considered nondiagnostic.

Results: Between September 2012 and December 2016, a total of 158 patients (median age: 57 years, 64.5% women) underwent EUS-FNA with an average of three needle passes for every lesion. The median lesion size was 17 mm. There were 113 mesenchymal neoplasms confirmed by immunohistochemistry (66 leiomyomas, 44 GISTs, two schwannomas, one leiomyosarcoma). The overall diagnostic yield of CBs was 84.17%. However, diagnosis was obtained in 98.5% (133/135) of the cases after exclusion of 23 cases in which EUS-FNA sampling was insufficient or without tumoural tissue. Only two mesenchymal neoplasms were not confirmed by CBs even after immunohistochemistry.

Conclusions: CBs collected by EUS-FNA and analysed by immunohistochemistry showed a high diagnostic yield in patients with mesenchymal neoplasms, even without on-site cytopathology.